1. Field of the Invention
The invention relates to a print head mechanism in a printer. More particularly, it relates to a floating print head mechanism attached to the printer lid so that new paper can be loaded into the printer without the cumbersome procedure of threading the paper through the print mechanism.
2. Description of the Related Technology
Printers are available in many different configurations utilizing a variety of technologies. The choice of the best features and technologies for a particular application depends on a number of factors including cost, print speed, print quality, durability and operating expenses. Regardless of the type of technology used, however, most printers have three elements in common: 1) a print head located on the side of the paper to be printed; 2) a platen located on the opposite side of the paper and providing physical support for the paper; and 3) a paper handling mechanism which moves the paper past the print head. In some cases the platen and the paper handling mechanism can be combined into a single roller which presses the paper against the print head and turns to advance the paper forward. This configuration is especially advantageous as it combines into a single item the functions of advancing the paper, providing a relatively hard surface against which the paper may be held, and maintaining the paper against the print head for a precision printing operation. Such rollers typically have a roller surface which is slightly compressible and which exhibits sufficient friction against the paper to move the paper with the required precision. Such rollers are well known in the printer industry and are not further described here.
Some printers will print on cut-sheet paper, which requires a complicated and expensive mechanism to pick up each new sheet and position it correctly underneath the print head. However, many inexpensive printers print on a continuous roll of paper or on a continuous stack of fan-fold paper. The low cost obtained by avoiding the use of the costly sheet-handling mechanism makes this approach ideal for such devices as label printers, adding machines, and point-of-sale receipt printers.
Maintaining print quality in roll-paper printers is usually accomplished by mounting the print head and the platen in a precise fixed relationship to each other, with the paper passing between them within a narrow space just large enough for the paper to pass through. However, when a new roll of paper must be inserted, this arrangement makes changing paper difficult. Not only must the user open the printer to access the paper space, but the user must also thread the new paper through the narrow space between the platen and the print head. This can be awkward and frustrating due to the cramped space allowed for the operator""s hands, the difficulty of inserting new paper into such a small space, and the problem of getting the paper aligned once it has been inserted.
This problem has been partially addressed in some conventional printers by providing print head mechanisms which can be moved away from the platen a small distance, thus slightly enlarging the space through which the paper must be threaded. This can be accomplished with a mechanism that raises the print head vertically upwards from the platen. It can also be accomplished by placing the print head on a short pivoting arm. However, maintaining accuracy dictates that the pivot arm be comparatively short and rigid, and that the pivot be relatively tight. A non-rigid arm can flex, thus introducing inaccuracy into the position of the print head. A long pivot arm amplifies manufacturing tolerances, thus requiring more expensive manufacturing techniques. Either approach adds components to the print head area, raising the cost and complexity of the resulting assembly. If the pivot joint is too loose, which is common with inexpensive pivot mechanisms, this too can create lead to inaccuracy in the print head/platen alignment. Thus, conventional printers require a tradeoff between low cost and the inconvenience of having to thread paper through a confined space whenever new paper is inserted in the printer. What is needed is a print head mechanisms that allows new paper to be inserted easily and quickly without threading paper through a narrow space, and without the expense of additional complex close-tolerance components for enlarging that space.
The invention includes a printer comprising a base with an attached lid having an open position and a closed position, a platen coupled to the base, a printhead assembly coupled to the lid, such that the printhead assembly is disposed proximate to the platen when the lid is in the closed position and is disposed apart from the platen when the lid is in the open position. The method of aligning the printhead with the platen in the printer comprises the steps of closing the printer lid onto the printer base, moving the printhead towards the platen when the lid is being closed, and aligning the printhead with the platen by contacting a printhead alignment edge with a guidepost alignment edge immediately before the lid closes.